1. Technical Field of the Intention
The present invention relates to a device for machining viscoelastic products: more precisely, it relates to a machine for machining and deflashing rubber products such as tires.
2. The Related Art
Tires are known to comprise a tread consisting of an outer layer of rubber-based mixtures, of greater or lesser thickness, in which are molded various grooves and tread patterns intended, inter alia, to improve the vehicle""s grip relative to the ground.
In certain cases, it is necessary to machine the outer surface of the tire: for example, to prepare for retreading of a worn tire or, indeed, to obtain a xe2x80x9cwornxe2x80x9d tire from a new tire, with a view to performing certain tests on the rigid belt, or on the carcass, without being hampered by the very considerable heating associated with the thickness of the rubber of the new tread during the tests.
In the first case (retreading), tires are often machined by abrasion (see for example International Publication No. WO 00/15388), but this process causes superficial heating which it is sometimes desirable to avoid. Moreover, a good surface state is sometimes required; a cutting process is then used. In general, the tire is made to turn about its axis and is moved towards the tool by translational movement of part of the frame (see for example U.S. Pat. No. 4,036,275).
The cutting tools used are generally cylindrical, that is to say, the cutting edge of the blade is circular (see for example U.S. Pat. No. 3,426,828 or U.S. Pat. No. 4,036,275) and the cut material passes inside the cylindrical tool and is discharged in the form of a strip.
When a patterned tire tread is machined by a cutting process, the formation of flash is noted to the rear of the tool at the edges of the grooves in the tire. Until now, this flash did not constitute a particular problem, but, confronted with increased quality requirements and the increasing severity of tests, it has become necessary to remove this flash in certain cases.
The invention relates to a machine for machining and for deflashing tire treads after a cutting machining operation which allows the same machine to be used for cutting and deflashing without having to remove the tire.
According to the invention, a machine for machining and deflashing tire treads comprises a frame, a drum for supporting the tire and rotating it about its axis, a cylindrical cutting tool and means for orienting the tool in various directions with respect to the tire, and further comprises means allowing rotation of the tire to be reversed and means for arranging the tool to work in two substantially symmetrical positions relative to the tire, a first position for cutting proper and a second position for deflashing, each of said positions corresponding to an opposite direction of rotation of the tire.
The machine according to the invention thus has the advantage of ensuring deflashing of the tire while retaining excellent machining precision. This is a substantial advantage over a machine which would require turning the tire round on its axis and causing it to turn in the reverse direction in front of the same tool, because removing and replacing the tire on its drum would involve loss of tire machining precision.
In a preferred variant, the tool comprises two circular cutting edges, each capable of occupying one of the two symmetrical positions.
Preferably, in the first position, the tool exhibits a cutting angle alpha and the tire an appropriate direction of rotation and, in the second position, the tool exhibits a cutting angle minus alpha and the tire the opposite direction of rotation to the above.
In another preferred variant, the cutting edge of the tool comprises at least one notch, that is to say, a portion having a lower axial length. This allows automatic division of the strip of cut material into shorter pieces and the prevention of jamming.
Of course, the machine according to the invention may be used in the conventional manner, that is to say, with a single machining stage, without then switching tool position and reversing tire rotation This is the case, for example, when the tire is being completely stripped of tread and there will not therefore be any flash to remove.